pyas2-lib

A pure python library for building and parsing message as part of the AS2 messaging protocol. The message definitions follow the AS2 version 1.2 as defined in the [RFC 4130][1].The library is intended to decouple the message construction/deconstruction from the web server/client implementation. The following functionality is part of this library:

• Compress, Sign and Encrypt the payload to be transmitted.
• Building the MIME Message from the processed payload.
• Building a signed MDN Messages for a received payload.
• Parsing a received MIME data and identifying if it as a Message or MDN.
• Decompress, Decrypt and Verify Signature of the received payload.
• Verify Signature of the received MDN and extract original message status.

Basic Usage

Let us take a look at how we can use this library for building and parsing of AS2 Messages.

Setup

• First we would need to setup an organization and a partner

  
  from pyas2lib.as2 import Organization, Partner

my_org = Organization( as2_name='my_unique_id', # Unique AS2 Id for this organization sign_key=b'signature_key_bytes', # PEM/DER encoded private key for signature sign_key_pass='password', # Password private key for signature decrypt_key=b'decrypt_key_bytes', # PEM/DER encoded private key for decryption decrypt_key_pass='password' # Password private key for decryption )

a_partner = Partner( as2_name='partner_unique_id', # Unique AS2 Id of your partner sign=True, # Set to true for signing the message verify_cert=b'verify_cert_bytes', # PEM/DER encoded certificate for verifying partner signatures encrypt=True, # Set to true for encrypting the message encrypt_cert=b'encrypt_cert_bytes', # PEM/DER encoded certificate for encrypting messages mdn_mode='SYNC', # Expect to receive synchronous MDNs from this partner mdn_digest_alg='sha256' # Expect signed MDNs to be returned by this partner )

### Sending a message to your partner

* The partner is now setup we can build and AS2 message
```python
from pyas2lib.as2 import Message

msg = Message(sender=my_org, receiver=a_partner)
msg.build(b'data_to_transmit')

• The message is built and now msg.content holds the message body and message.header dictionary holds the message headers. These need to be passed to any http library for HTTP POSTing to the partner.
• We expect synchronous MDNs so we need to process the response to our HTTP POST

  
  from pyas2lib.as2 import Mdn

msg_mdn = Mdn() # Initialize an Mdn object

Call the parse method with the HTTP response headers + content and a function that returns the related pyas2lib.as2.Messsage object.

status, detailed_status = msg_mdn.parse(b'response_data_with_headers', find_message_func)

* We parse the response mdn to get the status and detailed status of the message that was transmitted.

### Receiving a message from your partner

* We need to setup and HTTP server with an endpoint for receiving POST requests fro your partner.
* When a requests is received we need to first check if this is an Async MDN
```python
from pyas2lib.as2 import Mdn

msg_mdn = Mdn()  # Initialize an Mdn object
# Call the parse method with the HTTP request headers + content and a function the returns the related `pyas2lib.as2.Messsage` object.
status, detailed_status = msg_mdn.parse(request_body, find_message_fumc)

• If this is an Async MDN it will return the status of the original message.
• In case the request is not an MDN then pyas2lib.exceptions.MDNNotFound is raised, which needs to be catched and parse the request as a message.

  
  from pyas2lib.as2 import Message

msg = Message()

Call the parse method with the HTTP request headers + content, a function to return the the related pyas2lib.as2.Organization object, a function to return the pyas2lib.as2.Partner object and a function to check for duplicates.

status, exception, mdn = msg.parse( request_body, find_organization, find_partner, check_duplicate_msg)

* The parse function returns a 3 element tuple; the status of parsing, exception if any raised during parsing and an `pyas2lib.as2.Mdn` object for the message.
* If the `mdn.mdn_mode` is `SYNC` then the `mdn.content` and `mdn.header` must be returned in the response.
* If the `mdn.mdn_mode` is `ASYNC` then the mdn must be saved for later processing.  

## Contribute

1. Check for open issues or open a fresh issue to start a discussion around a feature idea or a bug.
1. Fork [the repository][2] on GitHub to start making your changes to the **master** branch (or branch off of it).
1. Create your feature branch: `git checkout -b my-new-feature`
1. Commit your changes: `git commit -am 'Add some feature'`
1. Push to the branch: `git push origin my-new-feature`
1. Send a pull request and bug the maintainer until it gets merged and published. :) Make sure to add yourself to [AUTHORS][3].

[1]: https://www.ietf.org/rfc/rfc4130.txt
[2]: https://github.com/abhishek-ram/pyas2-lib
[3]: https://github.com/abhishek-ram/pyas2-lib/blob/master/AUTHORS.md